Out of all of the processes involved in finishing with automatic taping tools, finishing corners is probably the toughest process to get down. This difficulty has led many to think that it's just better to coat angles by hand. This lengthy article is aimed at helping you finish corners with little to no touch up.
Have a good foundation
Glazing and finishing corners is a precision process, and the time you take in preparing corners, the taping mud you choose, the roller you use, what size and style taping head you use, the level of the quality of the tools you purchase... all of these things can play a significant role in what your finished product will look like, and how efficient your corner finishing system ends up being.
Take time to prep the corners
Take time to walk around the job and cut out bad board, scrape glue globs off, pre-fill gaps with a setting type joint compound, and set high screws. The time you spend here will not only save you time in the taping process, but will also make for less touch-up on sanding day.
Choose the right mud, and thin it down properly
We went over what mud to use in our "What joint compound should I use with the automatic taper?" article, and also went over how much water to use when taping corners in our "How much water should I add to my joint compound?" article, so if you haven't read those yet, we highly recommend that you do! In short, you will want to be able to thin your joint compound down significantly when taping corners, so you will need a joint compound with a high glue content so that your tape doesn't blister. Thinning your corner mud down significantly will also require you to pre-fill any gaps in the corner that are over 3/16" as you can get shrink cracks from taping over gaps with really wet mud.
What you are rolling with matters
Many times in the tool sale world we hear people say "it's just a roller... right?" implying that quality isn't a huge factor when it comes to what roller you use. Actually the roller you choose to use really can make or break your angles. A roller that doesn't seat the tape very tight to the corner can cause a few issues:
- If your tape is not rolled tightly to the corner, it can get snagged in the glazing process.
- You might not have enough mud to work with to sufficiently glaze over the top of the tape if it's all under the tape.
- An angle that has a bunch of mud behind the tape still is likely to sit higher, and require more mud to cover the tape. It can also cause a high corner which can be visible once it's painted.
Also always remember that rolling corners is like wiping tape in that you want to start in the center and work your way out to both ends. This will help eliminate bunching tape up. Folded and bunched up tape almost never covers completely with one pass of the corner box.
Your glazing process when taping is critical
Sometimes there can be a tendency to look at the taping process as not as critical as the finishing process with regard to how the tape looks. Meaning as long as the tape is applied properly, it doesn't have to be pretty because it will get 2-3 more finish coats. Though I understand this philosophy when it comes to flat and butt joints, this certainly should not be your mindset when glazing corners. The term glazing speaks to the fact that you want the excess mud that is pressed out by the roller to end up on top of the tape, not just to get wiped off. If you are aiming to only need to coat your angles one time after the tape coat, in a sense you should consider the process of glazing your corners as part of the finishing process.
One of the most critical things to pay particular attention to in the glazing process is the little bend in your glazing pole. This little bend can be used to apply more pressure to one half of the corner when needed. It can also allow you to apply more pressure to the bottom of your angle head where the bullet clip is which will reduce blade pressure and prevent wiping the tape too tight. Typically being at a 45 degree angle in relation to the corner is ideal, but it's not always possible because of small rooms or high ceilings etc. If you notice one side of the corner always seems lean, and the other side always seems full, try twisting the handle so that the little bend in the pole is pointing in the direction of the corner with more mud. This will help evenly distribute the mud on both side of the corner.
You also want to try to run your glazer clean so that you don't need to re-wipe every angle. The primary purpose of the angle head is to wipe in the angle for you. Aside from wiping the occasion glob of the wall, and wiping the intersections and bottoms of the corners, try not to wipe behind your glazer. Let it do it's job.
What you are glazing with matters
Expecting a quality finish out of your glazer means first of all that you want the right tool to glaze with. Though many have good results glazing with a flusher, I highly recommend glazing with an angle head. Though flushers are great in certain contexts and are a really affordable way to get started, the precision and consistency you will get out of an angle head will far outshine a flusher.
The other thing you will need to sort out is what size angle heads to use. The original design of angle heads was to tape with a larger head, and finish with a smaller head. Though that was the original design, many have found that the smaller the head, the more concentrated the mud will be, leaving you more coverage in the glazing process. The larger the head is, the more the compound feathered out away from the tape. This can be more beneficial in finishing the angle as the larger head helps hide any imperfections in the feather from your tape coat. I recommend glazing with a quality 2.5" angle head , and finishing with a quality 3.5" angle head. Many have also had great results taping with a 3" angle head and finishing with a 3.5" angle head.
Time to coat some angles
As you can see, more than half of this article has to do with your taping/glazing process. That's because glazing right is more than half the battle! If the glazing process was done poorly, coating your angles can be a pretty bumpy road. If you're striving for a legitimate finish grade glaze on your tape, coating them should be smooth sailing. On to coating some angles then right?
More prep work.
Yup, more prep work. Make sure to check the angles for globs or ridges. If needed, lightly sand or scrape them. Having dirty corners will cause you to pick up undesirable hitch-hikers in your angle head, which will require you to attempt to re run the angle again and again. After just one pass on an angle, the board starts to absorb moisture, so you will only get one or two more passes before you start balling the paper up on the drywall and making a real mess. One pass won't always get them full, but four passes will almost always make a mess. You want that second (or third) pass to be like glass so that you don't have to touch it with a knife. I recommend a light weight mud for low shrinkage, but the mud you use when coating angles in my opinion is far less crucial than what you tape angles with.
It's all about the pressure
Whether you are using a Mudrunner® or a corner box, the most important thing to remember when coating corners is to be mindful of what direction you are applying pressure in the corner. I can't remember how many times I have seen for example the top right side of all the vertical angles in the house with very little mud, and the top left side buried in mud. Many times this is merely an issue of where the operator is standing in relation to the corner, and which direction in the angle that he is applying pressure. For example in closets it's not uncommon to see the closet door wall side of the wall corners loaded with mud, and the side-wall side of the corner wiped completely tight. Most of the time, this is because of not being able to square up with the corner at a 45 degree angle.
When you are coating angles, and when you are glazing them, pay very close attention when you see one side of an angle that isn't coating well. Check and see if in that section of the angle, the other side seems to be buried in mud. In that section of the angle, position the tool in such a way that will apply more, if not all of the pressure to the side of the angle with extra mud.
Also, when running the corner box try to keep the corner box behind your body. This puts less pressure where the blades meet on the angle head, and leaves a little more mud.
Intersections
When coating in the intersections by hand, don't try to get right to them right away. Let the mud set up a little, say a solid 15 minutes to 1/2 hour depending on the climate. This will make it far easier to square up those intersections without wiping all the mud back out of the angle.
Also don't be afraid to go back and tighten the intersections up a day or two later when they are dry. This will make for a better intersection and save you time on sanding day.